Draft

ADVISORY BOARD ON 

RADIATION AND WORKER HEALTH

National Institute for Occupational Safety and Health 

Draft Review of ORAUT-OTIB-0078, Revision 03, Internal 

Dosimetry Coworker Data for the Feed Materials Production Center

Contract No. 211-2014-58081 

SCA-TR-2016-SP004, Revision 0 

Prepared by 

Bob Barton, CHP 

Harry Chmelynski, PhD 

SC&A, Inc.

1608 Spring Hill Road, Suite 400 

Vienna, Virginia 22182 

Saliant, Inc.

5579 Catholic Church Road 

Jefferson, Maryland 21755 

May 2016 

DISCLAIMER 

This is a working document provided by the Centers for Disease Control and Prevention (CDC) technical 

support contractor, SC&A for use in discussions with the National Institute for Occupational Safety and 

Health (NIOSH) and the Advisory Board on Radiation and Worker Health (ABRWH), including its 

Working Groups or Subcommittees. Documents produced by SC&A, such as memorandum, white paper, 

draft or working documents are not final NIOSH or ABRWH products or positions, unless specifically 

marked as such. This document prepared by SC&A represents its preliminary evaluation on technical 

issues. 

NOTICE: This report has been reviewed to identify and redact any information that is protected by the

Privacy Act 5 U.S.C. § 552a and has been cleared for distribution.
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SC&A, INC.: Technical Support for the Advisory Board on Radiation & 

Worker Health Review of NIOSH Dose Reconstruction Program

DOCUMENT TITLE: 

Draft Review of ORAUT-OTIB-0078, Revision 03, Internal 

Dosimetry Coworker Data for the Feed Materials Production Center

DOCUMENT NUMBER/ 

DESCRIPTION: 

SCA-TR-2016-SP004

REVISION NO.: 0 (Draft, Initial Issue)

SUPERSEDES: N/A

EFFECTIVE DATE: May 12, 2016

TASK MANAGER: John Stiver, MS, CHP [signature on file]

PROJECT MANAGER: John Stiver

DOCUMENT

REVIEWER(S): John Stiver 

Record of Revisions 

Revision 

Number

Effective 

Date Description of Revision

0 (Draft) 05/12/2016 Initial issue
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TABLE OF CONTENTS

Abbreviations and Acronyms ..........................................................................................................4

Executive Summary.........................................................................................................................5

1.0 Introduction and Background ..............................................................................................6

2.0 SC&A Review of the HIS_20 ORAU Database..................................................................8

2.1 Comparison of Derived TWOPOS Distributions ....................................................8

2.2 Comparison of Revision 01 and Revision 03 Coworker Distribution ...................12

2.3 Examination of Comments Column in HIS_20 ORAU Database .........................16

2.4 Intake and Solubility Class Information ................................................................18

2.5 Questionable Sample Pairs Observed ....................................................................18

2.6 Consideration of Implementation Guidelines........................................................21

3.0 Summary Conclusion.........................................................................................................22

4.0 References..........................................................................................................................23
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ABBREVIATIONS AND ACRONYMS

ABRWH Advisory Board on Radiation Worker Health 

CL control limit

D days (solubility)

GSD geometric standard deviation

HIS Health Physics Information System 

MDA minimum detectable activity

μg/d micrograms per day

μg/l micrograms per liter

NIOSH National Institute for Occupational Safety and Health

ORAU Oak Ridge Associated Universities

ORAUT Oak Ridge Associated Universities Team

OTIB ORAUT Technical Information Bulletin

SEC Special Exposure Cohort 

TWOPOS time-weighted one person–one sample

W weeks (solubility)

Y years (solubility)
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EXECUTIVE SUMMARY

The National Institute for Occupational Safety and Health (NIOSH) approved Revision 03 of 

ORAUT-OTIB-0078, Internal Dosimetry Coworker Data for the Feed Materials Production 

Center (ORAUT 2015; hereafter referred to as “OTIB-0078”) which was put into effect on 

August 19, 2015. The release of this document was formally announced to the Advisory Board 

on Radiation Worker Health (ABRWH) during Meeting 108 on November 18, 2015 (ABRWH 

2015), at which time the Board tasked SC&A with the review of the revised document. This 

report presents the results of SC&A’s review of the revised coworker model, which identified 

two findings and six observations. These findings and observations are as follows: 

Finding 1: Although claimant favorable, the censoring of negative and zero bioassay results at 

the minimum observed positive value in a given year is inconsistent with the guidance provided 

in ORAUT-RPRT-0053, Revision 2, Analysis of Stratified Coworker Datasets (ORAUT 2014; 

hereafter referred to as “RPRT-0053”), which specifies that all negative bioassay values be 

censored at zero. Note that the treatment of negative, zero, and results less than the minimum 

detectable activity (MDA) is an ongoing topic of discussion with the Special Exposure Cohort 

(SEC) Issues Work Group. 

Finding 2: NIOSH should closely examine questionable bioassay pairs that demonstrate 

differences of exactly two orders of magnitude on the same day for the same worker to assure 

that all of the numerical results used in OTIB-0078 accurately reflect the daily excretion rates for 

monitored workers at Fernald and are being interpreted correctly. 

Observation 1: SC&A was able to recreate the annual daily excretion rates reported in Table 2-3 

of OTIB-0078 with a reasonable degree of accuracy for most years. However, SC&A was not 

able to recreate the values reported for the years 1986–1997. These years appear to contain large 

numbers of censored results, which may have resulted in the employment of alternate methods to 

arrive at the daily excretion rates reported. If an alternate calculation approach was, in fact, used, 

OTIB-0078 would benefit from a discussion of how annual excretion data were derived, the 

rationale behind the approach, and ultimate effect on derived intakes. 

Observation 2: A comparison of the median urinary excretion rates derived in Revision 03 of 

OTIB-0078 (using the TWOPOS method) with the excretion rates calculated in Revision 01 of 

OTIB-0078 (using the pooled sample approach) showed very little difference. However, as 

expected, the use of TWOPOS methods results in a significant reduction in the variability of the 

derived distributions, and thus excretion rates at the 84th percentile were markedly lower using 

the TWOPOS method. 

Observation 3: Sample results that were below the detection limit were not reported in a 

consistent fashion in the HIS_20 ORAU database. NIOSH has elected to treat negative and zero 

results by censoring the value at the lowest observed positive result by year. This approach is 

claimant favorable compared to using the negative and zero values as is although not consistent 

with the methodology in RPRT-0053 (see Finding 1). 
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Observation 4: NIOSH appears to have used reported values at the MDA/control limit (CL) in 

situations where a lower numerical result was provided in the comments section of the bioassay 

entry. This is a claimant favorable interpretation of these records. 

Observation 5: SC&A observed 313 sample entries that should likely have been removed from 

the coworker model due to comments indicating the sample was an invalid result or the sample 

was for pre-employment/re-employment purposes. Given the relatively small incidence of such 

samples, the cumulative effect of excluding those results is likely to be insignificant.

Observation 6: OTIB-0078 would benefit from a discussion of the additional intake information 

(intake pathway and solubility type) available in the HIS_20 ORAU database. Neither the 

pedigree and accuracy of such indicators, nor whether appropriate adjustments to the intake 

model may be warranted, are not known at this time. 

1.0 INTRODUCTION AND BACKGROUND

Internal monitoring data are available for Fernald in a large electronic database, HIS_20 ORAU

(ORAUT n.d.), which contains nearly 436,000 individual bioassay results spanning from the 

early 1950s through October 2006. The vast majority of these entries are urinalysis samples that 

provide results in the units of micrograms of uranium per liter (μg/l). However, a small fraction 

of entries remained that are not relevant to the development of a uranium coworker model and 

were removed from the dataset prior to intake modeling. 

Per OTIB-0078, the available data were selected based on the criteria shown in Table 1. As part 

of its review, SC&A recreated these “scrubbing” steps and indicates how many records were 

removed from the model (see right-hand column in Table 1). 

Table 1. Description of Data Removal Steps Described in OTIB-0078 

Step Description of Entries Removed Entries 

Remaining

1 Initial full dataset 435,982

2 Not labelled as urinalysis 431,016

3 Not labelled as “U-Total” or “U-238” 429,328

4 Coded as “10, 5C, 70, VF, VR, and VE” 403,181

5 Units not equal μg/l 403,166

6 Results given as “N/A” 403,027

Although it was not stated directly in OTIB-0078, SC&A assumed that entries with blank dates, 

nonsensical dates, or results that were before 1952 were also removed. Based on these criteria, 

SC&A arrived at a final dataset of 403,016 entries. This is very close to, but does not exactly 

match, the number reported in OTIB-0078 (403,015). 

In addition to the scrubbing steps described above, OTIB-0078 states the following about 

bioassay results that were listed as equal to or less than zero:

For years with uncensored data, values less than or equal to zero were treated as 

being censored at the lowest positive value in that year for TWOPOS 
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implementation, however, values equal to the lowest positive value are still 

considered to be uncensored.

No other adjustments to the raw dataset were specifically discussed in OTIB-0078. 

As indicated in the transcript from Meeting 108 of the ABRWH (ABRWH 2015), the internal 

uranium coworker model was mainly revised to incorporate a time-weighted one person–one 

sample (TWOPOS) approach to analyzing the available data. To arrive at a TWOPOS value for a 

given worker, the following steps must be taken per RPRT-0053 (ORAUT 2014): 

1. For an individual worker, average all samples taken on a single day.

2. Weight each sample in a given year by the number of days that have passed since the

previous sample, or alternately the number of days since January 1 if it is the first sample

in the year.

3. For the period of time after the last sample in a given year, two methods are employed

depending on the circumstance:

a. If the worker provided a bioassay sample in the following year, that value is

assumed for the remaining period of time in the previous year.

b. If no sample is available in the following year, the value of the last sample in the

year under consideration is assumed for the remaining time.

A hypothetical example of this type of calculation is provided in Table 2 for clarity to the reader.

Table 2. Example of TWOPOS Calculation for a Hypothetical Worker 

Date of Sample Actual 

Result Units TWOPOS Calculation

TimeWeighted 

Result

1/10/1966 10 μg/l (Jan. 10, 1966 – Jan. 1, 1966 + 1) × 10 100

7/23/1966 15 μg/l (July 23, 1966 – Jan. 10, 1966) × 15 2,910

10/4/1966 5, 10a

a There were two samples on this date.

μg/l (Oct. 4, 1966 – July 23, 1966) × ((10 + 5) / 2) 547.5

11/25/1966 20 μg/l (Nov. 25, 1966 – Oct. 4, 1966) × 20 1,040

2/5/1967 5 μg/l (Dec. 31, 1966 – Nov. 25, 1966) × 5 180

1966 TWOPOS 

Value — — (100 + 2,910 + 547.5 + 1,040 + 180) / 365 13.1

Note that if there had not been a bioassay sample in 1967, the final sample in 1966 (20 μg/l on 

November 25, 1966) would have been weighted by the remaining time in the year. This would 

have resulted in the final time-weighted value increasing by a factor of 4, and the TWOPOS 

value for 1966 would increase from 13.1 to 14.6. 

Although not specific to OTIB-0078 and Fernald, SC&A observed what could be considered an 

unintended consequence when applying Step 3.a of the TWOPOS calculation. Specifically, one 

particular worker had his or her final sample for Year 1 on February 15; the next sample 
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observed was not until November 2 of Year 2. This results in the single sample being weighted 

by 319 days in Year 1 and 306 days for Year 2 (625 total days). 

In another example, the final sample for Year 1 was on December 15, and the next observed 

sample was not until January 17 of Year 3 (a combined 398 days between the two samples). In 

this case, no TWOPOS value would be calculated for Year 2, and the Year 1 TWOPOS would 

post-weight1 the last sample in Year 1 even though far fewer days had passed between the two 

samples than in the first example. 

1 Note: “Post-weighting” refers to weighting the sample by the number of days remaining in that specific year in 

addition to the pre-weighting.

One potential alternative would be to set a limit on the number of days that can pass between 

samples for the purposes of calculating TWOPOS results (in the worst case scenario, 730 days 

could potentially pass between sample results and still be used in the TWOPOS calculation). 

Certainly, one could argue that a sample taken 730 days after the last monitoring result may not 

accurately represent the intake potential for the entire intervening period. In this case, a postweighted result might be more appropriate for the TWOPOS calculation. 

An alternate variation might be to allow for a TWOPOS result to be calculated for a year with no 

actual sample results, provided there is a sample in the following year that is sufficiently close to 

the unmonitored year. This would allow for a TWOPOS result to be included even though the 

worker was technically unmonitored during the second year. 

SC&A concedes that any combination of rules adopted to perform the TWOPOS calculation will 

necessarily result in some samples being unintendedly biased; however, alternate methods of 

interpreting the one person–one sample statistic may be beneficial to explore. Regardless, the

potential issue is universal to the formation of all coworker models and is not specific to Fernald 

or OTIB-0078. Thus, further discussion beyond the general concept is not warranted in this 

report. 

2.0 SC&A REVIEW OF THE HIS_20 ORAU DATABASE

2.1 COMPARISON OF DERIVED TWOPOS DISTRIBUTIONS

SC&A analyzed the available dataset using the criteria specified in OTIB-0078 with one 

exception. As described in the previous section, OTIB-0078 states that bioassay samples that are 

listed as zero or less than zero (negative) are evaluated at the lowest positive value for that 

particular year. A review of the calculation files provided by NIOSH, as well as the data in 

HIS_20, indicate that the following minimum positive values were used by year (see Table 3 and 

Figure 1). As seen in Table 3 and Figure 1, many years had a minimum positive result of 1 μg/l, 

although a minimum value of 0.01 μg/l was observed as early as 1953.

2 The lowest annual 

positive bioassay value (0.001 μg/l) was observed starting in 1997.

2 See Section 2.4 for a discussion of questionable bioassay results on the order of one hundredth of a μg/l. 
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Table 3. Censoring Level by Year Used to Modify Zero and Negative Bioassay Results 

Year Result Year Result Year Result Year Result Year Result

1952 1 1963 1 1974 1 1985 1 1996 0.8

1953 0.01 1964 1 1975 1 1986 1 1997 0.001

1954 0.01 1965 0.01 1976 1 1987 3 1998 0.001

1955 0.19 1966 0.01 1977 1 1988 3 1999 0.001

1956 1 1967 1 1978 1 1989 5 2000 0.001

1957 0.49 1968 1 1979 1 1990 5 2001 0.001

1958 1 1969 0.8 1980 1 1991 7 2002 0.001

1959 0.17 1970 1 1981 1 1992 9 2003 0.001

1960 0.01 1971 1 1982 0.002 1993 0.8 2004 0.001

1961 1 1972 1 1983 1 1994 0.8 2005 0.001

1962 0.07 1973 1 1984 1 1995 0.8 2006 0.001

Figure 1. Censoring Level by Year Used to Modify Zero and Negative Bioassay Results

0.0001

0.001

0.01

0.1

1

10

1952195419561958196019621964196619681970197219741976197819801982198419861988199019921994199619982000200220042006

RPRT-0053, Revision 02 (ORAUT 2014) states the following about the treatment of negative 

values: 

When negative results are present they are censored at 0 and the mean is 

calculated in a similar fashion (Examples D, E, F, and G). 

The examples identified in the quoted text are shown in Figure 2. It is clear that the effect of 

censoring negative and zero bioassay results at the minimum observed positive bioassay result 

for the year would result in a claimant-favorable TWOPOS value. Nonetheless, the practice 

appears to be inconsistent with guidance provided in RPRT-0053. 

Finding #1: Although claimant favorable, the censoring of negative and zero bioassay 

results at the minimum observed positive value in a given year is inconsistent with the 
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guidance provided in ORAUT-RPRT-0053, Revision 2, Analysis of Stratified Coworker 

Datasets (ORAUT 2014), which specifies that all negative bioassay values be censored at 

zero. Note that the treatment of negative, zero, and results less than the MDA is an ongoing 

topic of discussion with the SEC Issues Work Group.

Figure 2. Screenshot from RPRT-0053 Providing Examples of How Negative Values Are 

Interpreted in the TWOPOS Calculation

In calculating the annual TWOPOS values, SC&A followed the guidance provided in 

RPRT-0053 and set all negative values to zero. This allows for an assessment of the effect that 

censoring negative and zero values at the minimum positive bioassay result has on the resulting 

annual TWOPOS values. Figure 3 shows a comparison of the TWOPOS values reported in 

OTIB-0078 with the values calculated by SC&A. 
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Figure 3. Comparison of the Calculated Logarithmic Geometric Mean TWOPOS Values 

from ORAUT 2015 and SC&A Evaluation 

0

5

10

15

20

25

30

35

40

45

50

Annual TWOPOS Result (μg/d)

Year

SC&A LOG GM NIOSH LOG GM

As seen in Figure 3, SC&A’s calculated TWOPOS values closely mirror the values reported in 

OTIB-0078 for most years. As one would expect, the SC&A values are slightly lower in some 

years, which is likely due to the differences in treatment of negative and zero values. However, 

the differing treatment of negative and zero values does not appear to be a significant 

contributing factor to the calculated annual TWOPOS values. 

There do appear to be significant differences in calculated values in the late 1980s and early-tomid 1990s. Aside from the treatment of negative values and zeros, SC&A did not identify 

distinct differences in the treatment of the data for these years upon inspection of the calculation 

files provided by NIOSH. It is important to note that the treatment of negative and zero bioassay 

samples would logically result in an increase in calculated TWOPOS values results in OTIB0078 when compared to the methods employed by SC&A. However, the opposite appears to be 

true for these years. Additionally, OTIB-0078 has adopted to exclude the data from 1991–1993 

due to the increased censoring level and has adopted to apply the intakes derived from earlier 

years for this period. This issue is discussed in detail in Section 2.2 of OTIB-0078. 

Nonetheless, the discrepancy in calculated values between NIOSH and SC&A for these years 

warrants further investigation. One possibility is that the data for these years were treated 

differently than for the other years due to the large number of results that appear to be censored

at a certain level. Although not discussed (nor referenced) in OTIB-0078, the analysis may have 

employed methods described in ORAUT-RPRT-0044, Analysis of Bioassay Data with a 

Significant Fraction of Less-Than Results (ORAUT 2009a; hereafter referred to as 

“RPRT-0044”).
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Observation 1: SC&A was able to recreate the annual daily excretion rates reported in 

Table 2-3 of OTIB-0078 with a reasonable degree of accuracy for most years. However, 

SC&A was not able to recreate the values reported for the years 1986–1997. These years 

appear to contain large numbers of censored results, which may have resulted in the 

employment of alternate methods to arrive at the daily excretion rates reported. If an 

alternate calculation approach was, in fact, used, OTIB-0078 would benefit from a 

discussion of how annual excretion data were derived, the rationale behind the approach, 

and ultimate effect on derived intakes.

2.2 COMPARISON OF REVISION 01 AND REVISION 03 COWORKER

DISTRIBUTION

The uranium urinalysis data in the HIS_20 ORAU database for Fernald were analyzed by 

NIOSH in 2007. The results of that analysis were reported in a draft white paper (ORAUT 2007) 

reviewed by SC&A. The same uranium coworker models were reported in OTIB-0078, 

Revision 01 (ORAUT 2010). The coworker model analyses reported in these documents follow 

the statistical procedure that was recommended at that time in ORAUT-OTIB-0019, Revision 01, 

Analysis of Coworker Bioassay Data for Internal Dose Assignment (ORAUT 2005). This 

procedure is commonly referred to as the “pooled” approach, as it fits each bioassay sample into 

the coworker distribution without any averaging or time-weighting steps. 

The procedure for removing unwanted records from the HIS_20 ORAU database for the OTIB0078, Revision 01 study was very similar to the OTIB-0078, Revision 03 procedure described 

above in Section 2.1. In Revision 01, coworker model distributions were developed by fitting a 

lognormal model to the individual urinalysis sample values for all workers in each quarter of 

each year, with a few exceptions noted below. 

A comparison of the OTIB-0078, Revision 01 quarterly coworker models with the annual 

TWOPOS models presented in OTIB-0078, Revision 03 was conducted using simulation of the 

Revision 01 quarterly models. For each year, 5,000 random samples from each of the four 

quarterly lognormal distributions were combined into a single annual distribution. The 50th and 

84th percentiles of the simulated annual distributions developed from the Revision 01 quarterly 

coworker models are listed in Table 4. The Revision 01 analysis developed only a single annual 

coworker model for the years 1952, 1953, 1994, 1995, and 1996, and the Revision 01 annual 

model percentiles are shown in Table 4 for these years. No models were reported in Revision 01 

for the years 1991, 1992, and 1993. The analysis for the year 1997 included three models, one 

for the months January through May and the other two for the final two quarters of the year. 

The plot in Figure 4 shows a comparison of the new TWOPOS Revision 03 84th percentiles with 

the annual 84th percentiles simulated using the Revision 01 quarterly models for the entire 

period 1952 through 2006. This plot uses a log scale for the vertical axis. A similar plot with a 

linear vertical scale is shown in Figure 5 for the years 1952 through 1990. The Revision 03 

TWOPOS estimates fall below the Revision 01 84th percentile estimates, except in the early 

years 1952 and 1955 and in the period from 1987 through 1997, where the Revision 03 

TWOPOS analysis yields higher estimates than Revision 01. The differences are more apparent 

in Figure 7, which contains plots of the 1952 through 1990 data using a linear scale. 
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The plots in Figures 6 and 7 show similar comparisons of the 50th percentiles (median). The 

50th percentiles match very well in both figures, except in 1952 and in the late 1980s through 

mid-1990s, where the Revision 03 TWOPOS analysis yields higher results than Revision 01. As 

expected, the use of TWOPOS does not have an appreciable effect on the estimates of the 

median. 

In Figure 8, the plots of the geometric standard deviations (GSDs) show larger differences 

between the two analyses. The TWOPOS procedure uses the average of all samples in a given 

year for each individual. As expected, the averaging process reduces the variability inherent in 

the individual sample values, resulting in the marked reduction in the coworker model GSD 

shown in this figure. 

Observation 2: A comparison of the median urinary excretion rates derived in Revision 03 

of OTIB-0078 (using the TWOPOS method) with the excretion rates calculated in 

Revision 01 of OTIB-0078 (using the pooled sample approach) showed very little 

difference. However, as expected, the use of TWOPOS methods results in a significant 

reduction in the variability of the derived distributions, and thus excretion rates at the 84th

percentile were markedly lower using the TWOPOS method. 
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Table 4. Simulated Annual Percentiles for OTIB-0078 Revision 01 Quarterly Coworker 

Models

Year

50th 

Percentile 

(μg/d)

84th 

Percentile 

(μg/d)

Year

50th 

Percentile 

(μg/d)

84th 

Percentile 

(μg/d)

1952 15.84 61.41 1978 5.94 13.08

1953 21.75 68.86 1979 6.05 14.08

1954 26.93 82.41 1980 5.90 14.16

1955 40.87 113.45 1981 3.75 9.58

1956 32.87 85.86 1982 4.89 11.62

1957 21.67 64.08 1983 4.83 12.37

1958 14.28 39.35 1984 5.18 12.60

1959 14.64 37.66 1985 5.01 10.86

1960 20.71 45.74 1986 3.13 7.36

1961 19.40 38.35 1987 1.89 5.20

1962 13.64 31.19 1988 1.88 4.27

1963 14.10 32.11 1989 0.35 1.52

1964 12.72 32.27 1990 0.48 2.06

1965 9.10 25.81 1994 0.01 0.06

1966 6.58 25.49 1995 0.01 0.07

1967 7.41 19.34 1996 0.01 0.04

1968 6.43 17.14 1997 0.01 0.04

1969 5.84 14.98 1998 0.02 0.08

1970 4.70 11.34 1999 0.02 0.08

1971 6.21 15.91 2000 0.02 0.10

1972 5.89 16.34 2001 0.05 0.17

1973 7.00 19.34 2002 0.05 0.14

1974 6.65 16.79 2003 0.05 0.14

1975 7.14 17.34 2004 0.05 0.13

1976 6.68 15.87 2005 0.07 0.18

1977 5.72 13.18 2006 0.07 0.17
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Figure 4. Comparison of 84th Percentiles 1952 to 2006 (log scale) 

0.01

0.1

1

10

100

1950 1960 1970 1980 1990 2000 2010

Uranium Excretion Rate 

(μg/d)

OTIB78-Rev1

OTIB78-Rev3

Figure 5. Comparison of 84th Percentiles 1952 to 1990 (linear scale) 

0

25

50

75

100

125

1950 1960 1970 1980 1990

Uranium Excretion Rate 

(μg/d)

OTIB78-Rev1

OTIB78-Rev3

Figure 6. Comparison of 50th Percentiles 1952 to 2006 (log scale) 

0.01

0.1

1

10

100

1950 1960 1970 1980 1990 2000 2010

Uranium Excretion Rate 

(μg/d)

OTIB78-Rev1

OTIB78-Rev3
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Figure 7. Comparison of 50th Percentiles 1952 to 1990 (linear scale) 

0

10

20

30

40

50

1950 1960 1970 1980 1990

Uranium Excretion Rate 

(μg/d)

OTIB78-Rev1

OTIB78-Rev3

Figure 8. Comparison of Geometric Standard Deviations (GSDs) 1952 to 2006 

1

2

3

4

5

6

7

1950 1960 1970 1980 1990 2000 2010

Geometric Standard Deviation 

(GSD)

OTIB78-Rev1

OTIB78-Rev3

2.3 EXAMINATION OF COMMENTS COLUMN IN HIS_20 ORAU DATABASE

The HIS_20 ORAU database contains a “comments column” that contained a non-blank entry in 

approximately one-third of samples used in building the uranium coworker model (130,203 of 

403,016 usable samples). In the vast majority of these cases, the entry would simply contain a 

sample number or other notation that does not affect the actual numerical result. However, a few 

of the comment entries had information that was relevant to the actual use of the sample itself. 

These comment entries fell into the categories listed in Table 5. 
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Table 5. Description and Number of Observed Comments That Are Relevant to the Use of

the Reported Sample Result

Comment Description Sample Result Reported Count

Comment indicates “below detection limit” “MDA/CL” listed as the sample 

result

1,699

Comment indicates “below detection limit” “Zero” listed as the sample result 1,525

Comment indicates an actual numerical 

sample result below the MDA/CL

“MDA/CL” listed as the sample 

result

715

Pre-Employment or Re-employment Not relevant to discussion 142

Visitor Not relevant to discussion 2

Possibly Invalid Sample Not relevant to discussion 169

As seen in the first three entries of Table 5, samples that were less than the MDA/CL or below 

the detection limit were not always treated in the same manner in the HIS_20 ORAU database. 

For example, the first two categories contained notations in the comments column that indicated 

the individual sample was below the detection limit. However, in some of these cases, the 

MDA/CL was used as the reported numerical result, while in others the sample was entered as 

zero. This inconsistent characterization of samples that were below the MDA in HIS_20 ORAU

is somewhat obviated by the fact that OTIB-0078 treated all negative and zero entries at the 

minimum observed positive result for that year. 

A third variation on the treatment of values that appear to be less than the MDA/CL was 

observed in which the comments column contains an individual numerical result that was less 

than the assumed MDA/CL; however, the MDA/CL was entered as the sample result. SC&A’s 

review of calculation files provided by NIOSH indicates that, in these cases, the MDA/CL value 

was used as is and no adjustment appears to have been made using the sample result provided in 

the comments column. This treatment would result in higher TWOPOS values and thus is 

claimant favorable.

Observation 3: Sample results that were below the detection limit were not reported in a 

consistent fashion in the HIS_20 ORAU database. NIOSH has elected to treat negative and 

zero results by censoring the value at the lowest observed positive result by year. This 

approach is claimant favorable compared to using the negative and zero values as is 

although not consistent with the methodology in RPRT-0053 (see Finding 1). 

Observation 4: NIOSH appears to have used reported values at the MDA/CL in situations 

where a lower numerical result was provided in the comments section of the bioassay entry. 

This is a claimant favorable interpretation of these records.

It can be seen in Table 5 that 142 samples contained a notation indicating it was a preemployment or re-employment sample. In addition, two samples had comments indicating the 

worker was a visitor from the Mound Plant. Per the instructions contained in Section 2.1 of 

OTIB-0078, these samples should likely have been removed prior to the TWOPOS analysis. 

Finally, 169 samples contained comments that indicate the sample result is likely invalid. For 

example, a notation might indicate that a sample was lost or not submitted; however, the result 
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was still reported as zero. This type of invalid result would bias the calculated TWOPOS values 

low. On the other hand, sample results were observed in which the comment entry indicated the 

result was a false positive. Inclusion of these samples would logically bias the calculated 

TWOPOS result high. Given the relatively small number of such observations, the cumulative 

effect of excluding these results is assumed to be insignificant. 

Observation 5: SC&A observed 313 sample entries that should likely have been removed 

from the coworker model due to comments indicating the sample was an invalid result or 

the sample was for pre-employment/re-employment purposes. Given the relatively small 

incidence of such samples, the cumulative effect of excluding those results is likely to be 

insignificant.

2.4 INTAKE AND SOLUBILITY CLASS INFORMATION

The HIS_20 ORAU database contains two columns that often indicate a specific type of intake 

(inhalation or ingestion3

) and/or the solubility class (days, weeks, or years) associated with a 

given sample. Approximately 81.5% of the observed samples indicated the exposure was from 

an inhalation compared to 5.5% reported as ingestion. The remaining 13% did not indicate an 

intake pathway. All 403,016 samples listed a solubility type, with the vast majority indicating 

solubility type W (weeks). Less than 0.002% were reported as solubility type D (days), with the 

remaining indicating solubility type Y (years). 

3 The database actually labels such results as “injestion” [sic] and so could alternately represent an injection or 

puncture wound-type dose.

SC&A is unaware of the pedigree or accuracy of this additional intake information associated 

with the available bioassay data. OTIB-0078 would benefit from a discussion of this information 

and whether adjustments to the coworker model, such as separating samples based on the intake 

pathway indicated and/or calculating separate TWOPOS distributions based on solubility type, 

would be appropriate. 

Observation 6: OTIB-0078 would benefit from a discussion of the additional intake 

information (intake pathway and solubility type) available in the HIS_20 ORAU database. 

Neither the pedigree and accuracy of such indicators, nor whether appropriate 

adjustments to the intake model may be warranted, are not known at this time.

2.5 QUESTIONABLE SAMPLE PAIRS OBSERVED

SC&A observed situations where two distinct sample entries are available for a single worker on 

the same day with results that are exactly two orders of magnitude different. One such example 

is given below for a worker in 1965 (see Table 6). It is not uncommon at a site such as Fernald 

for a worker to have multiple samples taken on the same day and for the results to be somewhat 

different. For example, a worker may have submitted a sample right at the start of the shift and 

then again at the end of a shift. However, consistently different by two orders of magnitude may 

indicate one of the entries is questionable. 

Another example of this type of record is provided in Table 7. In this case the worker had three

bioassay results per day for three consecutive days. The three samples on the first day vary from 
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0.01 to 11 μg/l (over three orders of magnitude). It is also worth noting that the higher sample is 

also marked as an “injestion” intake of solubility type Y. For the other two days, the samples 

marked as an “injestion” intake of solubility type Y was identical to the inhalation intake of 

solubility type W when also identified as sample type “3R.” The results that are labelled as 

sample type “XX” were two orders of magnitude lower. This highlights the need to understand 

and correctly interpret the numerical bioassay results contained in HIS_20 ORAU. 

It is especially important to evaluate the questionable bioassay pairs for their validity in light of 

the use of the minimum positive value observed by year to adjust negative and zero results. For 

example, the lowest positive value observed in 1965 and 1966 was 0.01 μg/l (see Table 3, 

Section 2.1). Each observed sample at this magnitude during those years was also paired with a 

result a factor of 100 higher (1.0 μg/l) on the same day. 

Finding 2: NIOSH should closely examine questionable bioassay pairs that demonstrate 

differences of exactly two orders of magnitude on the same day for the same worker to 

assure that all of the numerical results used in OTIB-0078 accurately reflect the daily 

excretion rates for monitored workers at Fernald and are being interpreted correctly.
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Table 6. First Example of a Worker with Multiple Bioassay Results on the Same Day that Are Two Orders of Magnitude 

Different

TYPE_ 

BIOASSAY

ACT_

UNITS

_SU

NUC_NA

ME

SAMPLE_

DATE

SAMPLE

_TYPE 

SAMPLE_

NUMBER

ACTIVITY COMMENTS INTAKE NUC_

CLASS

TYPE_INTAKE DATE_I

NTAKE

URINALYSIS ug/l U-TOTAL 01-Dec-65 XX 0.01 W INHALATION 01-Dec-65

URINALYSIS ug/l U-TOTAL 01-Dec-65 5B 1 W INHALATION 01-Dec-65

URINALYSIS ug/l U-TOTAL 01-Dec-65 XX 0.09 W INHALATION 01-Dec-65

URINALYSIS ug/l U-TOTAL 01-Dec-65 5B 9 W INHALATION 01-Dec-65

URINALYSIS ug/l U-TOTAL 01-Dec-65 XX 0.21 W INHALATION 01-Dec-65

URINALYSIS ug/l U-TOTAL 01-Dec-65 50 21 W INHALATION 01-Dec-65

URINALYSIS ug/l U-TOTAL 01-Dec-65 XX 0.36 W INHALATION 01-Dec-65

URINALYSIS ug/l U-TOTAL 01-Dec-65 5H 36 W INHALATION 01-Dec-65

URINALYSIS ug/l U-TOTAL 01-Dec-65 XX 1 W INHALATION 01-Dec-65

URINALYSIS ug/l U-TOTAL 01-Dec-65 5H 100 W INHALATION 01-Dec-65

Source: Reproduced from ORAUT n.d.

Table 7. Second Example of Worker with Multiple Bioassay Results on the Same Day that Are Two to Three Orders of 

Magnitude Different

TYPE_ 

BIOASSAY

ACT_

UNITS

_SU

NUC_NA

ME

SAMPLE_

DATE

SAMPLE

_TYPE 

SAMPLE_

NUMBER

ACTIVITY COMMENTS INTAKE NUC_

CLASS

TYPE_INTAKE DATE_I

NTAKE

URINALYSIS ug/l U-TOTAL 14-Dec-65 XX 0.01 W INHALATION 14-Dec-65

URINALYSIS ug/l U-TOTAL 14-Dec-65 3R 1 W INHALATION 14-Dec-65

URINALYSIS ug/l U-TOTAL 14-Dec-65 00 11 Y INJESTION 14-Dec-65

URINALYSIS ug/l U-TOTAL 15-Dec-65 XX 0.04 W INHALATION 15-Dec-65

URINALYSIS ug/l U-TOTAL 15-Dec-65 00 4 Y INJESTION 15-Dec-65

URINALYSIS ug/l U-TOTAL 15-Dec-65 3R 4 W INHALATION 15-Dec-65

URINALYSIS ug/l U-TOTAL 16-Dec-65 XX 0.02 W INHALATION 16-Dec-65

URINALYSIS ug/l U-TOTAL 16-Dec-65 00 2 Y INJESTION 16-Dec-65

URINALYSIS ug/l U-TOTAL 16-Dec-65 3R 2 W INHALATION 16-Dec-65

Source: Reproduced from ORAUT n.d.
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2.6 CONSIDERATION OF IMPLEMENTATION GUIDELINES

SC&A acknowledges that at the time OTIB-0078 was drafted, Revision 4.1 of the Draft Criteria 

for the Evaluation and Use of Coworker Datasets4

4 Also commonly referred to as the “Coworker Implementation Guidelines.”

 (NIOSH 2015) had not yet been accepted by 

the ABRWH for widespread use. Subsequently, the Board has tasked NIOSH/Oak Ridge 

Associated Universities (ORAU) with utilizing the implementation guideline on a trial basis for 

coworker modeling at Savannah River Site and Idaho National Laboratory. Should the Board 

ultimately accept the implementation guideline for widespread use, OTIB-0078 may have to be 

revised to reflect the new coworker requirements/criteria.

These criteria include, but are not necessarily limited to:

• Data adequacy and completeness

• Evaluation of stratification

• Appropriate time intervals for evaluation (e.g., quarterly versus annual)

• Applicability of available monitoring data to unmonitored workers

Given the large number of samples and coverage of workers monitored for uranium at Fernald, 

SC&A feels it is very unlikely that a legitimate data completeness or applicability of modeled 

doses to unmonitored workers issue (criteria bullets 1 and 4) would arise going forward. It 

should be noted, however, that there is currently an approved SEC that includes all 

subcontractors at Fernald from 1953 to 1983, due to the inability to reconstruct intakes of 

uranium for that individual subgroup of workers. 

Stratification considerations could become important to the higher exposure job types, such as 

chemical operators and other radiation workers who were consistently exposed at a higher level. 

However, often times these concerns are alleviated by specifying what types of workers should 

be assigned the 95th percentile intake rates versus the 50th percentile rates, which utilize an 

associated GSD. 

Finally, it was noted that Revision 01 of OTIB-0078 (ORAUT 2010) was evaluated on a 

quarterly basis instead of an annual basis. Revisions 02 and 03 of OTIB-0078 (ORAUT 2012 and 

2015, respectively) expanded the evaluation period to an annual basis. Given the large amount of 

data available for analysis, Fernald may be one of the few sites able to evaluate excretion data for 

intervals smaller than a year.
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3.0 SUMMARY CONCLUSION

Based on its review of Revision 03 of OTIB-0078, SC&A identified two findings and six

observations. The first finding identified apparent inconsistencies in the methods outlined in 

RPRT-0053 and those described in OTIB-0078. The second finding related to questionable 

sample results in which samples on the same day were observed to be different by a factor of 

exactly 100. The validity and interpretation of these results should be clarified.

The first observation describes the results of SC&A’s reconstruction of values reported in 

OTIB-0078 according to the TWOPOS methodology. Although SC&A was able to match the 

annual excretion values shown in OTIB-0078 for most years, several years in the late 1980s and 

1990s were not able to be recreated by SC&A. The source of this discrepancy has not been 

definitely established at this time; however, one likely possibility is the use of alternate methods 

such as those presented in RPRT-0044. 

Observation 2 compared the derived urinary excreta distributions between Revision 01 and 

Revision 03 of OTIB-0078. Interestingly, the use of TWOPOS methods did not appear to have a 

significant effect on the median urinary excretion rates. Not surprisingly, use of the TWOPOS 

methods resulted in a marked decrease in the variability of the derived excreta distributions, and 

thus observed 84th percentile values were lower in Revision 03. 

Observations 3–5 describe information contained in the comments column associated with each 

bioassay sample, including: 

• Inconsistent reporting/treatment of values below the detection limit in the HIS_20 ORAU

database (see Observations 3 and 4)

• Entries that are likely inappropriate for use in a coworker model due to indications of an

invalid result or association with pre-employment or re-employment (see Observation 5)

The last observation noted that the HIS_20 ORAU database contains additional intake 

information, beyond the individual sample result, including solubility type and intake pathway. 

This information should be explored to determine if it can be used to produce a more 

scientifically accurate and defensible coworker model (see Observation 6).

The final section provides some general commentary about ongoing discussions and 

developments in coworker implementation policy. However, as these policies and guidelines 

have not yet been accepted by the ABRWH for universal application, the discussion is provided 

for informational purposes only. 
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4.0 REFERENCES

ABRWH 2015. Transcript of the 108th Meeting of the Advisory Board on Radiation Worker 

Health, Advisory Board on Radiation Worker Health. November 18, 2015. 

NIOSH 2015. Draft Criteria for the Evaluation and Use of Coworker Datasets, Revision 4.1, 

National Institute for Occupational Safety and Health, Division of Compensation Analysis and 

Support. March 12, 2015. 

ORAUT 2005. Analysis of Coworker Bioassay Data for Internal Dose Assignment, ORAUTOTIB-0019, Revision 01, Oak Ridge Universities Team, Oak Ridge, Tennessee. October 7, 

2005. 

ORAUT 2007. Uranium Bioassay Study for FEMP – A Proposed Attachment for ORAUT-TKBS0017-5, Rev 1, Oak Ridge Associated Universities Team. November 6, 2007. 

ORAUT 2009. Analysis of Bioassay Data with a Significant Fraction of Less-Than Results, 

ORAUT-RPRT-0044, Revision 00, Oak Ridge Associated Universities Team. August 7, 2009. 

ORAUT 2010. Internal Dosimetry Coworker Data for the Fernald Environmental Management 

Project, ORAUT-OTIB-0078, Revision 01, Oak Ridge Associated Universities Team, 

Cincinnati, Ohio. June 3, 2010. 

ORAUT 2012. Internal Dosimetry Coworker Data for the Fernald Environmental Management 

Project, ORAUT-OTIB-0078, Revision 02, Oak Ridge Associated Universities Team, 

Cincinnati, Ohio. December 12, 2012. 

ORAUT 2014. Analysis of Stratified Coworker Datasets, ORAUT-RPRT-0053, Revision 02, 

Oak Ridge Associated Universities Team, Cincinnati, Ohio. October 8, 2014. 

ORAUT 2015. Internal Dosimetry Coworker Data for the Feed Materials Production Center, 

ORAUT-OTIB-0078, Revision 03, Oak Ridge Associated Universities Team, Cincinnati, Ohio. 

August 19, 2015. 

ORAUT n.d. HIS_20 ORAU, Health Physics Information System – Access Database, Oak Ridge 

Associated Universities Team. Undated.